intro story Coast / Estuary

Coast / Estuary

Coastal systems are among the most dynamic physical systems on earth and are subject to a large variety of forces. The morphodynamic changes occurring to coastlines worldwide are of great interest and importance. These changes occur as a result of the erosion of sediments, its subsequent transport as bed load or suspended load, and eventual deposition. 
 
Estuaries are partly enclosed water bodies that have an open connection to the coast. Estuaries generally have one or more branching channels, intertidal mudflats and/or salt marshes. Intertidal areas are of high ecological importance and trap sediments (sands, silts, clays and organic matter).
Within the Delft3D modelling package a large variation of coastal and estuarine physical and chemical processes can be simulated. These include waves, tidal propagation, wind- or wave-induced water level setup, flow induced by salinity or temperature gradients, sand and mud transport, water quality and changing bathymetry (morphology). Delft3D can also be used operationally e.g. storm, surge and algal bloom forecasting. 
 
On this discussion page you can post questions, research discussions or just share your experience about modelling coastal and/or estuarine systems with Delft3D FM. 
 

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Sub groups
D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems

 

 

Message Boards

water exchange modeling

Dr. Ahmed S. M. Ahmed, modified 8 Years ago.

water exchange modeling

Youngling Posts: 17 Join Date: 3/24/11 Recent Posts
Dears,

I am modeling a hydrodynamic of a tidal channel where a causeway with two openings shall be constructed across this channel. I introduced tracer (dye) and check the time for decaying such tracer.

Surprisingly, I found the tracer decays faster in the case of causeway compared to the case without causeway. The attached file shows the temporal variation of the tracer (5kg/m3 as initial condition and 1kg/m3 as a background), the black line represents the waterway without causeway and the red line represents the case with causeway with two opening.

Do you know the reason for that?

Kind Regards
Ahmed Sayed

Attachments:

Bert Jagers, modified 8 Years ago.

RE: water exchange modeling

Jedi Knight Posts: 201 Join Date: 12/22/10 Recent Posts
Dear Ahmed,

It's difficult to understand what's going on without more pictures of for instance the geometry pre and post construction, tidal and fluvial data, etc. hence my answer remains fairly general.
I would recommend to look at an animation of the dye over the simulation period for the case with and without dye. If you have map-files with data at the same time series then you may also consider to use the File Diff option (see File menu) of QUICKPLOT and animate the difference in dye between the two simulations.

Speculation: The causeway will affect the flow pattern upstream of the causeway. Since the causeway has two openings, it may due to flow differences create a kind of recirculation that stimulates a circulation of flow in the area where the dye is released. It is remarkable how well the minimum dye amounts still match, so it looks as if the dye tries to leave the measurement area but is largely prevented from flowing back in via the causeway openings whereas it was able to do so in the reference case.

Success,

Bert
Dr. Ahmed S. M. Ahmed, modified 8 Years ago.

RE: water exchange modeling

Youngling Posts: 17 Join Date: 3/24/11 Recent Posts
Dear Bert,

I am attaching animation files of dye decay for three cases, existing condition without causeway, two-opening causeway and three-opening causeway. Please look at these files and advise since it should be noted that the existing and the case with three opening causeway should be fast in decaying dye compared the case with two-opening causeway.

Kind Regards
Ahmed Sayed